A typical LED module includes a substrate, electrodes located on the substrate and at least a light emitting diode (LED) electrically connected to the electrodes. In order to achieve a large illumination area, a lens is provided to match with the LED to modulate the light distribution of the LED. The lens can distributes the light emitted from the LED to thereby illuminate a large area. However, part of the light emitted from the LED is reflected back by light emerging faces of the lens.